Guide
How to check unit economics with ChatGPT
ChatGPT or Claude can recompute your unit economics from your own numbers and show where they flatter you. Give it sales and marketing spend, new customers for the same period, average revenue per account, cost of revenue and monthly churn, and ask for each formula worked out: CAC as total sales and marketing spend divided by new customers; gross margin; customer lifetime as one divided by monthly churn; LTV as monthly revenue per account times gross margin times lifetime; LTV to CAC; and CAC payback in months. Then ask it to flag the usual mistakes: LTV on revenue instead of margin, ad spend passed off as CAC, spend and customers from different periods, churn based on too little data. The common reference points, LTV to CAC above 3 and payback under 12 months, assume margin-based figures.
Short answer
- Every formula shown, from your numbers.
- LTV on gross margin, not revenue.
- CAC with all sales and marketing spend.
- Mistakes flagged, inputs checked by you.
The brief to copy
Unit economics brief
"Recompute our unit economics from these numbers and show every formula.
CAC = sales and marketing spend ÷ new customers, same period. Say what spend was included; if it's only ads, call it paid media CAC.
Gross margin = (revenue − cost of revenue) ÷ revenue. Flag if hosting, payment fees or support are missing from cost of revenue.
Lifetime (months) = 1 ÷ monthly churn. LTV = average revenue per account per month × gross margin × lifetime. If our LTV uses revenue without margin, show both.
LTV ÷ CAC, and CAC payback = CAC ÷ (monthly revenue per account × gross margin).
List every definitional issue, then our figure against yours for each metric.
Numbers and our current figures: [paste]"
A worked example
Illustration: a made-up business. A startup's investor deck says LTV 8,000, CAC 750, LTV to CAC 10.7. Its numbers for the quarter: ad spend 30,000, sales salaries 30,000, 40 new customers, 200 a month per account, 75% gross margin, 2.5% monthly churn.
From the check
CAC: the deck's 750 is ad spend only (30,000 ÷ 40), so it's paid media CAC. With sales salaries: 60,000 ÷ 40 = 1,500.
Lifetime: 1 ÷ 2.5% = 40 months.
LTV: the deck's 8,000 is 200 × 40, on revenue. On margin: 200 × 75% × 40 = 6,000.
LTV to CAC: 6,000 ÷ 1,500 = 4.0 (the deck says 10.7).
Payback: 1,500 ÷ (200 × 75%) = 10 months.
Issues that matter most: LTV on revenue; CAC without sales salaries.
A ratio of 4.0 and a 10-month payback are what the deck should show; 10.7 overstated the ratio more than twice over. The founder checks the churn figure covers at least six months before putting the new numbers in the deck.
Before you use the numbers
- Check each input against your books and the same period.
- Use margin-based LTV in anything you show investors.
- Watch churn based on fewer than six months; lifetime will be too long.
- Keep the deck and the model consistent after the fix.
- Save the brief for next quarter.
Next step: a project that knows your numbers
Pasting the same figures every quarter gets old. A Claude project for founders keeps your metrics, plan and rules in one place, so every check and investor update starts from them.
Skills for this
- FinanceUnit economics checkChecks CAC, LTV, LTV to CAC, payback, and gross margin from your numbers, shows each formula, and flags definitional mistakes that inflate results.
- FinanceFinancial model assumptions reviewReviews a financial model's assumptions: lists each with its source, tests sensitivity, checks plausibility against history, and names the 3 that matter.
- FinanceCash runway updateWrites a cash runway update: cash, 3-month average net burn, runway in months, base, downside and upside scenarios, and levers, formulas shown.
- FinanceMonthly investor updateWrites a short, honest monthly investor update: summary, KPIs, highlights, lowlights with cause and fix, cash and runway, and specific asks.
Questions
Can ChatGPT calculate unit economics?
It can recompute them from your numbers and show each formula: CAC as sales and marketing spend divided by new customers in the same period, LTV as monthly revenue per account times gross margin times lifetime, LTV to CAC, and CAC payback in months. Ask it to flag definitions that inflate results, then check the inputs yourself.
Should LTV use revenue or gross margin?
Gross margin. LTV on revenue overstates what a customer is worth, because it ignores what it costs to serve them. The common LTV-to-CAC reference point of 3 assumes margin-based LTV.
What is a good CAC payback period?
Under 12 months is commonly cited as healthy for SaaS, and enterprise sales often run longer. Compare your figure with your own target and how much cash you have, rather than with a benchmark alone.
AI skill
Have your AI check whether each customer makes you money
Put this skill in AI Skill Pod and everyone on your team gets it in their Claude, Cursor or ChatGPT (Pro, Business, Enterprise): one invite link, free to start. Unit economics check has your AI recompute CAC, gross margin, LTV, LTV to CAC and payback from your numbers, show every formula, and flag the definitional mistakes that make the results look better than they are.
14 days free · No card needed
Sources
- David Skok, For Entrepreneurs: SaaS metrics 2.0 — LTV on gross margin; LTV to CAC above 3; CAC recovered within 12 months (read 2026-11-04)
- David Skok: SaaS metrics 2.0, definitions (read 2026-11-04)
- Wall Street Prep: Months to recover CAC (read 2026-11-04)
- a16z: 16 startup metrics (read 2026-11-04)